1. Field of the Invention
Exemplary aspects of the present invention relate to a fixing device and an image forming apparatus, and more particularly, to a fixing device for fixing a toner image on a recording medium and an image forming apparatus including the fixing device.
2. Description of the Related Art
Related-art image foaming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium (e.g., a transfer sheet) according to image data. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
In one example of the fixing device, a heater serving as a fixed member provided inside a loop formed by a belt member is pressed against a rotary member opposing the belt member to form a nip portion between the belt member and the rotary member. Together, the belt member heated by the heater and the rotary member apply heat and pressure to a recording medium bearing a toner image to fix the toner image on the recording medium as the recording medium passes through the nip portion.
However, over time, as an inner circumferential surface of the belt member slides over the heater, the heater and the belt member may experience wear due to friction generated therebetween. Further, substantial resistance between the belt member and the heater, again due to friction generated therebetween, may require great driving torque, which may in turn pose a risk of generating faulty toner images due to slippage of the belt member, damage to drive gear teeth, or both.
To address those problems, the fixing device may include a low-friction sheet member to reduce the friction of contact between the belt member and the heater. Thus, in one example, a halogen lamp is provided inside a rotary member outside a belt member. A pressing pad serving as a fixed member is provided inside a loop formed by the belt member and is pressed against the rotary member with the belt member in between to form a nip portion between the belt member and the rotary member. As the belt member and the rotary member rotate to nip and feed a recording medium bearing a toner image to fix the toner image on the recording medium, an inner circumferential surface of the belt member slides over the pressing pad. The low-friction sheet member is provided on a slide surface of the pressing pad, that is, a surface of the pressing pad that contacts the inner circumferential surface of the belt member, so that the inner circumferential surface of the belt member slides smoothly over the low-friction sheet member, that is, over the pressing pad. Such an arrangement can reduce wear of the belt member and the pressing pad.
The low-friction sheet member is typically formed of fluorocarbon resin fiber mesh. As such, the low-friction sheet member may not adhere to the pressing pad sufficiently, and therefore the low-friction sheet member may fall off the pressing pad or may be twisted or warped due to friction between the belt member and the low-friction sheet member. Consequently, the recording medium may be creased as the recording medium passes through the nip portion, resulting in formation of a faulty fixed toner image.
To address this problem, the low-friction sheet member may be attached to the pressing pad by using a holding member. However, such a compact mechanism as a fixing device can accommodate only a small holding member due to limited space.
Alternatively, the low-friction sheet member may be provided with a hole through which a screw is passed to secure the low-friction sheet member to the pressing pad. However, stress concentrated on the hole may deform the hole. As a result, the low-friction sheet member may be twisted or warped.